The objectives of this grant are to explore the immunomodulatory potentials of new classes of bifunctional proteins in defined ex vivo systems of T cell activation and in mouse models of autoimmunity. The present grant stems from our original observation several years ago that antigen-presenting cells (APC) can be converted into deletional APC, designated as "artificial veto cells (AVC)," that can inhibit antigen-specific T cells. Our AVC engineering approach involves expressing "coinhibitor" proteins on APC, which send inhibitory trans signals to T cells. Our unique angle entails the use of protein transfer (instead of gene transfer) as the preferred means for coinhibitor expression. Over the course of the current grant, both the protein transfer tools and the coinhibitors of choice have evolved, and significantly, two protein transfer modalities emerged midway through the last funding period: 1) a simple two-component protein transfer method that uses coinhibitor. Fcgamma1 :palmitated-protein A conjugates as "paints," and 2) a new class of soluble "trans signal converter proteins (TSCP)," which make possible the engineering of each "CoSR.COI TSCP" combines a costimulator receptor (that passively blocks its cognate ligand on APC) with a coinhibitor ligand (that actively sends an inhibitory trans signal to its cognate receptor on T cells). The first TSCP we developed, CTLA-4sFas ligand, proved to be 1000-fold more active than CTLA-4.lg (the most widely studied costimulator blocker). This renewal application offers three specific aims, which propose continuing the development of the therapeutic potential of the AVC concept and pursuing our promising immunomodulator candidates: 1) Extending the palette of TSCP beyond CTLA-4.FasL to enable the targeting of different APC-T cell combinations; 2) Comparing the immunomodulatory properties of various TSCP in autoimmune disease models; and 3) Leveraging the flexible Fcgamma1 fusion protein:palmitated-protein A and TSCP "painting" methods for unique immunobiological ends: costimulator: coinhibitor interplay, TSCP synergism, and T cell auto-stimulation, and reversal of TSCP function.